Splicing is a method for joining Fibre Metal Laminate (FML) panels in which, at the location of the joint, metal sheets are overlapped to form a Damage Tolerant (DT) bond. This joining method is successfully applied in aircraft structures, but has one main disadvantage; it cannot be used in structures with significant double curvature. To qualify FMLs for these specific locations as well, a different joining method is required. With this in mind, the idea of Friction Stir Welded (FSW-ed) FMLs was born. By FSW-ing individual metal sheets together before lay-up, it is possible to create FML structures with the required double curvature. This research was aimed at developing the DT design principles for successful application o f t h i s concept in aircraft structures. In order to reach this goal, a step-by-step DT compliance plan was created. This plan started with the identification of analytical methodologies for predicting the DT performance of the joint. In the following steps, the relations between the DT properties of FSW-ed Glare 3-3/2-0.4 and standard Glare 3-3/2-0.4 were determined experimentally, and used to design different concepts that met the requirements from the compliance plan. Out of the four concepts, the idea with the highest value in terms of cost-effectiveness was determined, which was subsequently compared to other materials typically used in the aerospace industry. Experimental results show that cracks grow faster inand residual strength is lower ofthe FSWed version of the laminate. To bring the DT performance back to the level of the standard laminate, additional layers of material are necessary at the location of the joint. The concept that does this in the most cost-effective way for Glare 3-3/2-0.4, is a joint with an inter-laminar aluminum doubler of the same thickness as the other metal layers. Compared to the spliced version of the laminate, the FSW-concept is significantly more expensive. When looking at the DT performance compared to other materials, only certain carbon-fibre reinforced plastics have better properties.